User account setting defaults should be editable in the ACP

In many cases, the board admin wishes to change some sort of default setting of his new users accounts. For example, he might wish to disable the default to notify the user upon replies or change the default post order for newly registered users. Currently, this can only be realized using an extension, which in my opinion is a total overkill.

Instead of defining defaults somewhere in the PHP code, the anonymous user (or potentially an additional special user for more flexibility) should be copied for each new user to determine what default values are used. This also ensures that the newly registered users receives the same default settings as he saw when browsing the board as a guest, while giving the administrator full control of the default values for a user.